A lighting unit including an LED light source and a plate-like lens body used in combination has conventionally been suggested (see, for example, Japanese Patent No. 4458359 (or U.S. Pat. No. 7,322,729 B2 corresponding thereto) which is referred to as patent literature 1 hereinafter).
As shown in FIGS. 1 to 3, a lighting unit 200 disclosed in Patent Literature 1 can include a plate-like lens body 210, and an LED light source 220 arranged to face the front surface of the lens body 210. The lens body 210 can be formed in a plate shape, and can have a front surface 211, a rear surface 212 opposite to the front surface 211, a first end surface 213 functioning as a light exiting surface having a substantially rectangular shape greater in width than in thickness, a second end surface 214 opposite to the first end surface 213, and total reflection surfaces 215a to 215e each arranged on an optical path of the rays of light emitted from the LED light source 220 and entering the lens body 210. As shown in FIG. 2A, the total reflection surfaces 215a to 215c are disposed between the optical axis AX of the LED light source 220 and the first end surface 213 so that part of rays of light Ray1 emitted from the LED light source 220 and entering the lens body 210 enters these surfaces 215a to 215c and travels between the optical axis AX of the LED light source 220 and the first end surface 213. As shown in FIG. 2C, the total reflection surfaces 215d and 215e are disposed between the optical axis AX of the LED light source 220 and the second end surface 214 so that part of rays of light Ray2 emitted from the LED light source 220 and entering the lens body 210 enters these surfaces 215d and 215e and travels between the optical axis AX of the LED light source 220 and the second end surface 214.
In the lighting unit 200 with the above configuration, as shown in FIG. 3, the part of rays of light Ray1 emitted from the LED light source 220 and entering the lens body 210 can travel between the optical axis AX of the LED light source 220 and the first end surface 213 and be totally reflected by the total reflection surfaces 215a to 215c, thereby exiting through the first end surface 213 (in particular, through the central region A1). Further, the part of rays of light Ray2 emitted from the LED light source 220 and entering the lens body 210 can travel between the optical axis AX of the LED light source 220 and the second end surface 214 and be totally reflected by the total reflection surfaces 215d and 215e, thereby exiting through the first end surface 213 (in particular, through the regions A2 adjacent to, and on both sides of, the central region A1). This configuration can allow the first end surface 213 (including the central region A1 and the adjacent regions A2) to form a linear light source for linearly emitting light.
However, the above lighting unit 200 should include a through hole H because the linear light emission should be achieved. Namely, with this configuration, the rays of light Ray1 can enter the total reflection surface 215b and 215c to be reflected therefrom to the wall surfaces H1 of the through holes H, and then can be reflected from the wall surfaces H1 toward the first end surface 213 (the central region A1), so as to exit from the first end surface 213 (the central region A1). This means that the portion to be formed into the through hole constituting the desired reflection surfaces should be ensured in the raw material lens body 210, and accordingly, the width W of the lens body 210 cannot be shortened by that amount. If the width W of the lens body 210 is simply shortened for compactness, the luminous flux exiting through the first end surface 213 may be reduced by that amount.